Nuclear power source

ABSTRACT

There is provided means for utilizing radioactive emission from a radioisotope to generate relatively high voltages at small current densities.

United tates Fatent Round .Ettiy 18, B972 NUCLM POWER SOURCE [56]References Cited [72] Inventor: Kenneth J. Round, Ottawa, Ontario,UNITED STATES PATENTS Canada 2,824,246 2/1958 Keller ..310/3 0 3 A m E fa m Ob 2,864,012 Thomas 6! [7 1 ss'gnee tam, g g'ggi g g L M 3,189,7656/1965 Danko et a] ..310/3 x Filed: Jan- 3, 1970 Primary ExaminerRodneyD. Bennett, Jr.

Assistant ExaminerBrian L. Ribando [211 App! 6373 Attorney-Curtis,Morris and Safford [52] U.S. Cl. ..3l0/3 R, 136/202 [57] ABSTRACT gag S4 2 There is provided means for utilizing radioactive omission from aradioisotope to generate relatively high voltages at small currentdensities.

5 Claims, 1 Drawing Figure NUCLEAR POWER SOURCE This invention relatesto a nuclear electrical power source which has particular, but notexclusive application, in the utilization of beta-emittingradio-isotopes.

While the general principles upon which this invention operates arefairly well known, prior devices have not been commercially useful.

The present invention envisages the provision of an electrical powercell which may be manufactured with the minimum of close tolerancedimensions and which may be assembled quickly with utmost simplicity.The latter advantageous feature permits assembly with a minimum use ofremote manipulators. The invention in one embodiment also provides foraltering the output current level for different applications.

It is an object of one aspect of the invention to provide a simple,reliable, long-lived and robust source of high voltage electricity.

Although the invention is primarily directed to any novel integer orstep, or combination of integers or step, herein described and/or shownin the accompanying drawing, nevertheless according to one particularaspect of the invention to which, however, the invention is in no wayrestricted, there is provided a nuclear power source comprising a hollowmetallic body member, having a longitudinal axis and internal dimensionswhich are substantially constant along a major portion of said axis,vacuum-tight closure means for said body member at one end thereof, ahigh voltage insulator, vacuum sealed to the other end of said body, amounting post extending from the outside of said high voltage insulatorto the inside of said body member, said mounting post being parallel tosaid axis, said mounting post providing an output terminal, said bodymember providing an electrical return terminal, a plurality of isotopebearing plates disposed along and electrically connected to saidmounting post inside said body, and first spacing means between isotopebearing plates, said isotope bearing plates being electrically insulatedby said high voltage insulator and spaced from the interior of said bodymember, a plurality of collector plates interspaced with and insulatedfrom said isotope bearing plates, said collector plates beingelectrically connected to said body member, and second spacing meansbetween said collector plates, and means for evacuating said bodymember.

A preferred embodiment of the invention will now be described withreference to the accompanying drawing which shows, in cross-section, anuclear battery assembly.

Referring now to the drawing, the nuclear electrical power generator isgenerally indicated at l. The generator has a hollow cylindrical bodyconfiguration defined by a wall at least the interior dimensions of thecylinder being constant throughout the length of the cylinder. The base11 of the cylinder and the walls are formed of stainless steel but othermaterials of adequate biological shielding capability, against B andbremsstrahlung radiation, and mechanical strength may be used. The base11 is provided with an evacuation tube 13 which is crimped or weldedafter evacuation.

The top of the cylinder is provided with an insulator mounting flange12, formed of a suitable metal, and either brazed or welded to the bodywall 10. The flange has an inner wall 14 converging inwardly to receivean insulator 16 which is formed of a suitable material, such as alumina,and which is vacuum brazed to the flange 12. The insulator 16 is chosento withstand the required voltage under specified operating conditionssuch as temperature, relative humidity. The insulator 16 supports amounting post 18 which extends into the interior of the cylinder 1 andwhich is threaded as at 19. The mounting post carries upper and lowerinsulator discs 20, 22. Between these are a plurality of intermediatecollector plates 28 which are spaced apart by spacers 29. An additionalspacers 29 are disposed between the uppermost collector plate 24 andinsulator 20 and the lower collector plate 26 and the insulator 22. Thisincreases the effective leak path. These spacers are split so as to fitsnugly in the interior of the body 1. The insulators 20, 22 and thecollector plates 24, 26 and 28 are maintained in mechanical contact witheach other by nuts 30, 32 engaging the threaded portion 19 of themounting post 18. The collector plates 24, 26 and 28 make electricalcontact with the generator body 1. Vent holes 34 are provided in theinsulator discs 20, 22 to facilitate the evacuation process. Thecollector plates have relatively large apertures to adequately clear themounting post 18 and the spacers 92. A series of isotope bearing plates40, in number being one less than the number of collector plates, areelectrically connected to the mounting post 18 and are interspacedbetween the collector plate by spacers 42, the isotope bearing plates 40and their associated spacers being maintained in mechanical andelectrical contact with each other by means of a spring 44 disposedbetween the lower isotope bearing plate and the lower insulator 22. Itwill be noted that the isotope bearing plates 40 are so dimensioned asto provide an adequate gap between the edges thereof and the spacers 29.Plaques 46 of gettering material are attached to the inside surface of aspacer ring 29 and which are activated by heating during a bake-out andevacuation process after assembly, in a manner well known to thoseskilled in the art. A baffle 48 may be included to protect the upperinsulator disc 20 during the brazing or welding of the insulator 16.

A typical nuclear power cell in accordance with the embodimentdescribed, using 4 curies of promethium deposited on both sides of sevenisotope bearing plates of seven-eighths inch diameter, gave a shortcircuit current of 7.8 X 10' amperes and a Peak Open Circuit Voltage of13.5kV.

It is to be understood that the walls of the cylinder 1 may define around annulus or any other suitable cross-section which is substantiallythe same throughout the length of tubular portion of the body 1 occupiedby the collector plates 24, 26 and 28 and the insulator discs 20, 22.

Assembly of the nuclear power cell is rendered extremely simple by thenovel features of the construction. After selecting the number ofisotope bearing plates to be used, an appropriate number of collectorplates and spacers are obtained and these are threaded in order, ontothe mounting post, which is attached to the top insulator, together withthe upper and lower insulating discs and the top bafile. The assembly isthen held in coaxial relationship by the nuts engaging the threadedportion of the mounting post, and introduced into the cylinder. The topflange and top insulator are then brazed or welded together. Thecompletely assembled cell is then evacuated to a low pressure (10 mm.Hg) via the copper sealing tube and the assembly is baked-out and thegetters fired in the usual manner.

While promethium 147 has been described, this was used in view of itsrelative inexpensiveness, its useful half-life (2.6 years) and therelatively low energy of the emitted ,8 particles which minimizesshielding requirements. With such a beta emission the mounting rod takeson a positive polarity while the body has a negative polarity.Preferably all such isotopes should be pure beta emitters and should notresult in a decay product which is gaseous.

The invention represents a considerable advance in the art, in that:

A. The isotope is deposited on simple plates or cylinders which can beconveniently handled during the construction of the cell.

B. The structure can be modified by adding or removing basic componentswithout re-design. Thus cells with various outputs can be built at will.

C. The structure is self-aligning on insertion into the outer shell,minimizing the handling time during the assembly process and thusreducing the risk of radiation exposure. The structure also provides forautomatic alignment and assembly.

Other embodiments falling within the terms of the appended claims willoccur to those skilled in the art.

What is claimed:

1. A nuclear power source comprising:

i. a hollow metallic body member, having a longitudinal axis andinternal dimensions which are substantially constant along a majorportion of said axis,

lOl045 0382 ii. vacuum-tight closure means for said body member at oneend thereof,

iii. a high voltage insulator vacuum sealed to the other end of saidbody,

iv. a mounting post extending from the outside of said high voltageinsulator to the inside of said body member said mounting post beingparallel to said axis, said mounting post providing an output terminal,said body member providing an electric return terminal,

v. a plurality of isotope bearing plates disposed along and electricallyconnected to said mounting post inside said body, and first spacingmeans between isotope bearing plates, said isotope bearing plates beingelectrically insulated from the body member by said high voltageinsulator and spaced from the interior surface of said body member,

vi. a plurality of collector plates interspaced with and insulated fromsaid isotope bearing plates, said collector plates being electricallyconnected to said body member, and second spacing means between saidcollector plates, and

means for evacuating said body member.

2. A nuclear power source, as defined in claim 1 wherein said isotopebearing plates contain promethium 147.

3. A nuclear power source, as defined in claim 2 including a getter forimproving the vacuum.

4. A nuclear power source, as defined in claim 1 further including apair of insulator discs on said mounting post disposed longitudinallyoutside all of said isotope bearing plates and collector plates.

5. A nuclear power source, as defined in claim 4 further including abaffle disposed between one of said insulator discs and said highvoltage insulator.

lOl045 0383

1. A nuclear power source comprising: i. a hollow metallic body member, having a longitudinal axis and internal dimensions which are substantially constant along a major portion of said axis, ii. vacuum-tight closure means for said body member at one end thereof, iii. a high voltage insulator vacuum sealed to the other end of said body, iv. a mounting post extending from the outside of said high voltage insulator to the inside of said body member said mounting post being parallel to said axis, said mounting post providing an output terminal, said body member providing an electric return terminal, v. a plurality of isotope bearing plates disposed along and electrically connected to said mounting post inside said body, and first spacing means between isotope bearing plates, said isotope bearing plates being electrically insulated from the body member by said high voltage insulator and spaced from the interior surface of said body member, vi. a plurality of collector plates interspaced with and insulated from said isotope bearing plates, said collector plates being electrically connected to said body member, and second spacing means between said collector plates, and vii. means for evacuating said body member.
 2. A nuclear power source, as defined in claim 1 wherein said isotope bearing plates contain promethium
 147. 3. A nuclear power source, as defined in claim 2 including a getter for improving the vacuum.
 4. A nuclear power source, as defined in claim 1 further including a pair of insulator discs on said mounting post disposed longitudinally outside all of said isotope bearing plates and collector plates.
 5. A nuclear power source, as defined in claim 4 further including a baffle disposed between one of said insulator discs and said high voltage insulator. 